Indexing mechanism



June 14, 1966 R. A. FRITZ INDEXING MECHANISM 4 Sheets-Sheet 1 Filed Sept. 23, 1963 ROBERT A. FRITZ INVENTOR Mn )M A 77ORNEYS June 14, 1966 R. A. FRITZ 3,255,861

INDEXING MEGHANIS M Filed Sept. 23, 1963 4 Sheets-Sheet 4 ROBERT A. FRITZ INI/ENTOA fyuz/ United States Patent 3,255,861 INDEXING MECHANISM Robert A. Fritz, Fresno, Califl, assignor to Fresno Valves, Inc., Fresno, Caiif., a corporation of California Filed Sept. 23, 1963, Ser. No. 310,788 11 Claims. (Cl. 198-49) The present invention relates to an indexing mechanism for rotary tables and the like and more particularly to such an indexing mechanism providing 180 table movement.

The present invention is intended primarily for use with a cementitious pipe casting machine employing a rotary table to support a pair of pipe forming jackets. The jackets are positoned on the table 180 apart at a predetermined jacket loading and unloading position and a pipe casting position. The table is preferably rotated 180 between such positions to permit the casting of one length of pipe with the table being returnable 180 for the casting of a succeeding length of pipe. The opposite position is then located for ready removal of the previously cast length of pipe and for the placement of an empty pipe forming jacket in such location.

The majority of conventional cementitious pipe casting machines provide only a single pipe casting station. In such machines, the freshly cast length of pipe must be removed from the machine at the casting station and an empty pipe forming jacket repositioned only after complete removal of the previously cast length of pipe. Such operation is not only slow and tedious, but also increases the possibility of jarring the uncured length of pipe therein frequently causing damage or complete collapse of such pipe within the jacket. Of .the relatively few pipe casting machines employing indexing tables, the control mechanisms have been so complex and troublesome that their use has not been practical. One such machine employs an electric motor for driving the table with an electrically energized brake which is slow in operation and requires frequent servicing and Another machine employs a hydraulically actuated rotary arm which engages a single tooth on the table to provide a push-start for the table which then must be caught and stopped manually.

Therefore, it is a broad object of the present invention to provide an improved indexing mechanism for rotary tables.

Another object is to provide an improved indexing mechanism for rotary tables employed in cementitious pipe casting machines.

Another object is to provide such an indexing mechanism wherein the table is rotated between a pair of diametrically opposed work stations.

Another object is to provide an improved indexing mechanism capable of high speed rotation of a work table between such work stations.

Another object is to provide an indexing mechanism for rotary tables which is capable of such high speed rotation with a minimum of jarring, particularly during starting and stopping.

Another object is to provide a high speed indexing mechanism for a rotary work table having a control system operative to motivate the table with a single double acting hydraulic cylinder.

Other objects and advantages of the present invention will subsequently become apparent in the following description in the specification.

In the drawings:

FIG. 1 is a side elevation of a cementitious pipe forming machine having an indexing table with which the indexing mechanism of the present invention is associated.

FIG. 2 is a somewhat enlarged top plan view of the indexing table of FIG. 1..

replacement.

FIG. 3 is a somewhat enlarged bottom plan view of the indexing mechanism showing the control mechanism associated therewith.

FIG. 4 is a somewhat enlarged side elevation of the indexing and control mechanisms of FIG. 3.

FIG. 5 is a somewhat enlarged fragmentary perspective of the control lever portion of the indexing control mechanism of FIGS. 3 and 4.

FIG. 6 is a somewhat enlarged longitudinal section through the hydraulic cylinder of the indexing mechanism.

FIG. 7 is a diagrammatic view of the hydraulic control system associated with the hydraulic power cylinder of FIG. 6 shown in one operating position.

FIG. 8 is a diagrammatic view of the control system of FIG. 7 shown in another operating position.

FIG. 9 is a diagrammatic view of the control system shown in still another operating position.

Referring more particularly to the drawings, a cementitious pipe casting machine in which the indexing mechanism of the present invention is conveniently embodied is indicated generally at 10. The machine provides a circular walled frame 11 which circumscribes a compart ment 12 having an open upper end 14. A radially inwardly extended ledge or shelf 16 is rigidly mounted on the frame within the compartment 12 in downwardly spaced relation to the upper end 14 thereof. A plurality of rollers 17 are freely individually mounted on pairs of brackets 18 rigidly upstanding from the shelf 16.

A circular work support table 20 is disposed within the upper end 14 of the compartment '12 and has a downwardly opening circular grooved track to receive the rollers 17 which support the table 20 for rotation about a central substantially vertical axis indicated at 21 in FIG. 2. The table has an opposite upper surface 22 which has a pair of diametrically opposed work positions or stations, namely a casting station 24 and a loading station 25 individually superimposed on a pair of circular openings 26 and 27 extended through the table. The table 20 is adapted to support a clamping mechanism, not shown, about each of the openings 26 and 27 individually to hold a pair of cylindrical pipe forming jackets 30 in substantially erect position thereon, as shown in FIG. 1. A superstructure 32 is mounted on the frame closely adjacent to the compartment 12 to support a cementitious material pouring and tamping head 34 over the casting station 24 of the machine which forms no part of the present invention and is not described in detail.

The indexing mechanism embodying the principles of the present invention is generally indicated at 40 in FIG. 2 and provides a power unit 42 and a control unit 43. The power unit employs a double-acting hydraulic jack or motor 45 which, as best seen in FIG. 6, includes an elongated cylinder 46 having a reciprocable piston 47 disposed therein. The piston is closed at one of its ends by a cylinder mounting cap 48 and at its opposite end by a rod guiding cap 4?. The piston 47 has an integral elongated rod 50 having an enlarged diameter, frusto-conical, base portion 51 adjacent to and inclined toward the piston. The rod guide cap 49 has an internal annular chamber 52 which communicates with the interior of the cylinder 46 through a restricting annular orifice 54 which receives the base portion 51 of the piston rod 50. The mounting cap 48 provides a fluid passage 55 and the rod guide cap 49 has a fluid passage 56, both of which communicate with the interior of the cylinder. A mounting bracket 57 is rigidly connected to the outer end of the: rod 50 which, as best shown in FIG. 4, mounts an elongated cover 58. The cover, in the retracted position of the rod, is extended over the rod guide cap 49 and the cylinder 46 in spaced longitudinal alignment with the rod 50. When the rod is extended, the cover travels outwardly therewith to shield 3 the rod from loose pipe ttorming material which sometimes drops through the openings 26 and 27 in the table.

As best shown in FIGS, 3 and 4, the mounting cap 48 of the hydraulic motor 45 carries a mounting block 60 which receives a pivot pin 62. The pin is upwardly extended from a mounting platform 64 radially inwardly extended from the frame 11 into the compartment 12 in coplanar relation with the shelf 16. The bracket 57 on the rod 50 of the hydraulic motor is pivotally mounted on a pivot pin 65 disposed eccentrically of the axis 21 of the table by way of a bracket 66 bolted thereto.

The control unit 43 of the indexing mechanism 40 of the present invention provides a cam bracket 69 which, as best shown in FIGS. 3 and 4, is rigidly connected to the underside of the rod guide cap 49 of the hydraulic motor 45 and is outwardly extended therefrom in spaced substantially parallel relation to the table 20 beneath the rod 50 and rod mounting bracket 57. The cam bracket includes an elongated downwardly opening camming slot 70 having a pair of opposite off-set camming portions 71 and 72 concentrically disposed about the pivot pin 62 of the mounting block 60 which are interconnected by an intermediate inclined ramp portion 73.

The control unit 43 further provides a control valve mounting platform 75 which is disposed within the compartment 12 on the frame in downwardly spaced substantially parallel relation to the table 20 and in partially underlying relation to the camming bracket 69. A control lever 76 providing an intermediate body portion 77, an upper dog-leg portion 78, and a lower bifurcated arm 79 is pivotally mounted on the mounting board 75 in depending relation therefrom on a substantially vertical axis provided by a mounting pin 80. The upper dog-leg end 78 rotatably mounts a roller 82 Which is received within the camming slot 70 of the bracket 69.

The control unit 43 further includes a hydraulic actuating system which, as shown in FIG. -'7, includes a pair of control valves 84 and 85. The control valve 84 provides a valve body 86 which houses an elongated spool 87 for longitudinal reciprocal movement therein. The spool includes a plurality of longitudinally spaced annular lands 88 which are adapted in the conventional manner to direct hydraulic fluid through the valve in various paths incident to longitudinal positioning of the spool within the valve body 86. Such positioning of the spool is accomplished manually by an actuating handle 89 pivotally mounted on the valve body.

The control valve 85 includes a body portion 90 mounted on the platform 75 which houses an'elongated spool 91 having a plurality of longitudinally spaced annular lands 92 with the end lands providing longitudinal slots 93 therethrough. One end of the spool 91 is extended through the body 90 for pivotal connection at 94 to the bifurcated arm 79 of the control lever 76. The movement of the spool 91 is thereby automatically controlled by the position of the roller 82 within the cam ming slot 72.

The manual control valve 84 receives hydraulic fluid under pressure from a pump 95 through a main highpressure fluid supply conduit 96 which communicates with the interior of the valve body 86 at a position substantially intermediate its ends. A pair of interconnected drain lines 98 are connected to the valve body 86- individually adjacent to its ends to communicate said ends of the valve body with the tank 97. A pair of fluid conducting conduits 100 and 101 are individually connected to the valve body 86 in substantially diametrically opposed longitudinally spaced relation on opposite sides of the main supply conduit 96. The conduit 100 is connected to the valve body 90 of the automatic control valve 85 at a point substantially intermediate its ends. The conduit 101 is connected adjacent to each end of the valve body 90 by way of a branch conduit 102. A pair of cylinder supply conduits 105 and 106 are connected to the valve body 90* in diametrically opposed longitudinally spaced relation on opposite sides of the conduit 100 individually to connect the valve body 90 to the fluid passages 55 and 56 in the mounting cap 48 and the rod guide cap 49, respectively, of the hydraulic motor 45. A pair of bypass conduits 107 and 108 are disposed in interconnecting relation between the cylinder supply conduits 105 and 106. The 'by-pass conduits individually include oppositely operating one-way pressure relieving check valves 109 and 110.

OPERATION The operation of the described embodiment of the subject invention is believed to be clearly apparent and is briefly summarized at this point. As the jacket 30 shown in full lines in FIG. 1 is filled with cementitious material from the head 34 at the casting station on the machine 10, an empty jacket is placed over the opening 27 at the loading station 26 on the table 20. After the casting operation is completed, the control unit 43 is actuated to index the table 180 to interchange the relative positions of the openings 26 and 27 to position the empty jacket 30 beneath the head 34 at the casting station 25 and to position the filled jacket 30 at the loading and unloading station 26.

In order to accomplish such rotation of the table 20, the handle 89 of the manual control valve 84 is moved to the position shown in FIG. 7 to permit hydraulic fluid to flow under pressure in the direction of the arrows through the main supply conduit 96, the valve body 86, the supply conduit 100, to the valve body 90. Such flow is then directed through the cylinder supply conduit 105 into the rod end of the hydraulic motor by way of the passage 56. Fluid pressure is thereby directed against the end of the base portion 51 which, as shown in FIG. 7, is seated in closing relation with the orifice 54. With such fluid pressure acting on the relatively small areas of the base portion, the rod is accelerated slowly until the base portion is moved sufliciently to open the orifice 54 and allow fluid pressure to act upon the full area of the piston 47. Such gradual acceleration is provided by the inclined surface of the base portion which progressively opens the orifice and modulates the flow of fluid therepast. With such arrangement, the table is provided a smooth start from a stationary position so as not to disturb the uncured pipe in the jacket 30. With continued flow of fluid against the piston, the rod retracts into the cylinder 46 to rotate the table 20* in a counterclockwise direction, as viewed in FIG. 2. As retraction of the rod continues, the moment arm between the eccentrically disposed pivot pin and the axis 21 of the table decreases which causes a corresponding increase in table velocity. Also during such rotation of the table 20, the hydraulic motor 45 pivots about the pivot pin 62 in aclockwise direction, as viewed in FIG. 2, until reaching the fully retracted dead center position of FIG. 3 at which position the table attains its maxi- 'mum velocity. Also during such swinging movement,

the roller 82 of the control lever 76 rolls freely through the end 71 of the camming slot at which time the spool 91 of the automatic control valve is positioned, as in FIG. 7, to interconnect the supply conduits 100 and 105 through the valve body 90. At the fully retracted position of the rod 50, the inertia of the rotating table 20 carries the table and hydraulic motor 45 past the dead center position of FIG. 3. Concurrently, the roller 82 abuts the ramp portion 73 of the camming slot 70 to pivot the control lever 76 about its mounting pin 80. Such lever movement motivates the spool 91 within the body of the automatic control valve 85 toward the shifted position of FIG. 8. As the spool 91 approaches a centered position within the valve body 90, the fluid supply conduit and the cylinder conduits and 106 are momentarily opened to each other in order to equalize the fluid pressure at each end of the cylinder 46 to allow the hydraulic motor to coast by dead center.

When the spool 91 reaches the fully shifted position of FIG. 8, the flow of pressurized fluid is reversed from the direction shown in FIG. 7 to flow through the supply conduit 106 to the mounting cap end of the cylinder to extend the rod 50 outwardly therefrom. Such extension of the piston rod motivates the table 20 through its remaining 90 of rotation to complete the cycle.

As shown in FIG. 8, during extension of the piston rod 50, hydraulic fluid on the low pressure side of the piston is permitted to escape back to the tank 97 from the chamber 52, through the conduits 105 and into the valve body 90. Such exhaust fluid then flows through the slot 93 in the spool land 92 adjacent to the conduit 105 and thence to the tank by way of the conduits 102, 101 and 98. As the rod aproaches the fully extended position, the frusto-conical base portion 51 thereof enters the annular orifice 54 to restrict or modulate the exhaust flow from the cylinder. The back pressure on the piston is progressively increased by the inclined surface of the base portion of the rod gradually closing the orifice to cause a corresponding gradual decelerating and stopping of the table 20. The co-action between the base portion 51 of the rod 50 and the orifice 54 is thereby effective in both directions of rod movement to provide smooth gradual acceleration and deceleration of the table at each end of its travel. Should the' table meet an obstruction during travel of the piston 47 in either direction causing excessive high pressure in the supply conduits and cylinder 46, such pressure is relieved through the appropriate relief valve 109 or 110 which opens its respective bypass conduit 107 and 108 interconnecting the cylinder supply conduits 105 and 106.

After the desired manipulation of the jackets 30, as previous-1y described, the control unit 43 is actuated for returning the table 20 to its original position by re-positioning the handle 89 of the manually controlled valve 8 4 to the position shown in FIG. 9. Such re-positioning of the control valve 84 causes the fluid under pressure in the main supply conduit 96 to be reversed and fed once again through the cylinder supply conduit 105 and into the rod end of the hydraulic motor 45 to retract the piston rod 50. It is noted that the branch conduit .102 which in FIGS. 7 and 8 served as a drain line is now employed in FIG. 9 as a high-pressure fluid supply line to the cylinder 4'6 with the [formerly pressurized conduit 100 now serving as a drain line. Such actuation causes the table to be return-rotated in a clockwise direction, as viewed in FIG. 2, during which time the roller 82 of the control :lever 76 moves [freely through the end 72 of the canrming slot 70. As before, the lever is actuated upon abutment of the roller with the ramp portion 76 of the slot as the hydraulic motor swings past dead center to reverse the automatic valve and cause re-extension of the piston rod 50 within the cylinder 46. Upon nearing bull extension of the piston rod 50, the fluid escaping from behind the piston is again modulated by the base portion of the rod entering the orifice 54 to cushion and again bring the table to a gradual stop.

From the foregoing, it is readily apparent that the indexing mechanism of the present invention provides quick smooth-rotation of the indexing table 20 through 180 by the use of a single double-acting hydraulic motor. Such movement is accomplished in a minimum of time and avoids jarring ot the table by gradual acceleration and deceleration at its extreme limits of movement. After initial actuation of the manual control valve 84, the hydraulic motor is automatically controlled so as alternately to retract and extend to provide dull 180 rotation of the table with no additional manual manipulation.

Although the invention has been herein shown and described in What is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. An oscillating support comprising a table, means mounting the table for rotation about a predetermined axis between a pair of predetermined angularly related work positions, a single telescopically extensible and contraetible powered member having opposite ends, means pivotally anchoring an end of the powered member in radially spaced relation to the axis, and means pivotally connecting the opposite end of said powered member to the table at .a position eccentric thereto in substantially equal angular relation to the anchor means in said work positions of the table so that successive contract-ion and extension of the powered member oscillates the table from one work position to the other with maximum mechanical advantage at the initiation and conclusion of such movement and maximum angular velocity of the table midway between such initiation and conclusion of the movement.

2. An indexing mechanism comprising a frame having a substantially circular track, a circular table having a central axis and providing diametrically opposed work stations, roller means engaging said circular track mounting the table on the frame \for rotary movement about said central axis, and a single reciprocable powered member mounted on the frame having pivotal connection to said table at a position eccentrically ot" said central axis in predetermined angular relation to the table with the powered member being disposed in the same predetermined angular relation at both of said work positions of the table to motivate the table to interchange the positions of said work stations incident to reciprocation out said powered member.

3. An indexing mechanism comprising a frame having a substantially circular track, a circular table having a central axis providing diametrically opposed interchangeable work stations, rolle'r means engaging said circular track mounting the table on the lframe for rotary movement about said central axis, a single reciprooable powered member p-ivotally mounted on the frame having pivotal connection to said table at a position eccentrically of said central axis and providing a longitudinal axis disposed in substantially equal angular relation to an imaginary line between the axis of the table and said mounting of the powered member on the frame at said opposed work stations, and control means mounted on the frame having operational connection to said powered member to actuate the same as the table is motivated between .gaid work stations by reciprocation of said powered mem- 4. An indexing mechanism comprising a frame having a substantially circular track, a circular table having a central axis providing diametrically opposed interchangeable work stations, roller means engaging said circular track mounting the table on the frame for rotary movement about said central axis, an extendible-retractable member having an end pivotally mounted on the frame and an opposite end pivotally connected to said table at a position eccentrically of said central axis and said extendible-retractable member providing a longitudinal axis disposed in substantially equal angular relation to an imaginary line between the axis of the table and said end of the extendible-retractable member on the frame at said opposed work stations, and control means mounted on the frame having operational connection to said extendible-retractable member to actuate the same as the table is motivated beween said work stations by said extendible retractable member.

5. An indexing mechanism comprising a frame having a substantially circular track, acircular table having a central axis providing diametrically opposed interchange able work stations, roller means engaging said circular track mounting the table on the frame for rotary movement about said central axis between said work stations, an hydraulically powered jack having a cylinder end pivotally mounted on the frame and an opposite reciprocable rod end pivotally connected to said table at a position eccentrically of said central axis, said rod end of the jack being extended from said cylinder end with the table rested at said work stations, and the rod end being alternately retracted and return-extended to rotate the table to interchange such work stations with said jack being pivotally swung about said pivotal connection of the cylinder end thereof during such rotation of the table, control means mounted on the lframe, and earn means mounted on the jack adjacent to said rod end being eng ageable with said control means to control said reciprocation of the rod end of the jack incident to relative movement of the cam means with respect to the control means during swinging movement of the jack as the table is rotated.

6. An indexing mechanism comprising a frame having a substantially circular track; a circular table having a central axis providing diametrically opposed interchangeable work stations; roller means engaging said circular track mounting the table on the tframe tor rotary movement about said central axis between said work stations; ian hydraulically powered jack having :a cylinder end pivotally mounted on the frame and an opposite reciprocable rod end pivotally connected to said table at a position eccentrically of said central axis, said rod end of the jack :being extended from said cylinder end with the table rested at said work stations, and the rod end being alternately retracted and extended to rotate the table to interchange such work stations with said jack being pivotally swung about said pivotal connection of the cy linder end thereof during such rotation of the table, said jack having an intermediate dead center position with the rod end there-t fully retracted, with the pivotal connection of the rod end on the table, and the central axis of the table all being aligned; cam means mounted on said jack adjacent to-the rod end thereof for swinging movement with the jack during reciprocation of the rod end to rotate the table having an arcuately curved camming slot disposed therein concentrically with the pivotal connection of the cylinder end of the jack; an hydraulic control system having a pair of fluid directing valves for conducting fluid under pressure to said rod end of the jack for retracting the same to rotate the table; and a control lever connected to one of said valves mounting a roller for engagement with said camming slot in the camming bracket automatically to actuate the valve at said dead center position of the jack to open said cylinder and rod ends of the jack to each other to permit the inertia of the table to move the jack past said dead center position whereupon said valve is operative to deliver fluid under pressure to said cylinder end of the jack to extend said rod end to complete rotation of the table.

7. The indexing mechanism of claim 6 wherein said work stations are disposed 180 apart.

8. The indexing mechanism of claim *6 wherein said hydraulic jack has a cover member mounted on said rod end tor reciprocation therewith to shield the rod end from toreign material at said work stations.

9. An indexing mechanism comprising a table; means mounting the table for rotation about a predetermined 8 axis, the table having predetermined interchangeable work stations thereon substantiaily equally spaced from said axis and in predetermined angular relation about the axis; a longitudinally extensible and contractible drive member having opposite ends; means pivot-ally connecting an end of the drive member to the table eccentrically of said axis; anchor means pivotally anchoring the opposite end or said drive member at a position such that the anchor means, connecting means and axis may be aligned in bisecting relation to the angle between the work stations; and control means connected to the drive member adapted to cause said drive member alternately to contract and to expand in rotating the table to interchange said work stations.

'10. An indexing mechanism comprising a frame; a table mounted in the tframe for rotation about a predetermined substantially erect axis, the table having predetermined interchangeable work stations thereon in so stantially equally spaced relation (from the axis and in predetermined angular relation about the axis; a long-itudinally extensible and contractable drive member having opposite ends; means piv-otally connecting an end of the drive member to the table eccentrically of its axis; means anchoring .the opposite end of the drive member to the frame at a position such that the table can be rotated to a position in which the anchor means, connecting means and axis can be aligned in bisecting relation to the angle between the work stations; control means for the drive member mounted on the frame; and cam means movable with the table engageable with the control means to control the extension and contraction of the drive member incident to relative movement orf the cam and control means.

11. An indexing mechanism comprising a frame; a .table mounted on the frame \for rotation about a substantially erect axis; an hydraulically powered jack having a cylinder end pivotally mounted on the frame and an opposite reciprocable rod end pivotally connected to said table at a position eccentrically or said central axis, said rod end of the jack being extended from said cylinder end with the table rested at said work stations, and the rod end being alternately retracted and return-extended to rotate the table to interchange such work stations with said jack being pivotal-1y swung about said pivotal connection of the cylinder end thereof during such rotation of the table; control means mounted on the frame; and cam means mounted on the jack adjacent to said rod end being engageable with said control means to control said reciprocation of the rod end of the jack incident to relative movement of the cam means with respect to the control means during swinging movement of the jack as the table is rotated.

References Cited by the Examiner UNITED STATES PATENTS 363,114 5/1887 Burton s 104 49 2,073,862 3/1937 Bendix 104--38 2,253,548 8/1941 Allison 2989 2,528,985 11/1950 Wunsch 1 212-66 2,779,490 1/1957 Clarke.

3,067,726 12/1962 Williams 92 X 3,115,974 12/1963 Kovach.

MARVIN A. CHAMPION, Primary Examiner. 

1. AN OSCILLATING SUPPORT COMPRISING A TABLE, MEANS MOUNTING THE TABLE FOR ROTATION ABOUT A PREDETERMINED AXIS BETWEEN A PAIR OF PREDETERMINED ANGULARLY RELATED WORK POSITIONS, A SINGLE TELESCOPICALLY EXTENSIBLE AND CONTRACTIBLE POWERED MEMBER HAVING OPPOSITE ENDS, MEANS PIVOTALLY ANCHORING AN END OF THE POWERED MEMBER IN RADIALLY SPACED RELATION TO THE AXIS, AND MEANS PIVOTALLY CONNECTING THE OPPOSITE END OF SAID POWERED MEMBER TO THE TABLE AT A POSITION ECCENTRIC THERETO IN SUBSTANTIALLY EQUAL ANGULAR RELATION TO THE ANCHOR MEANS IN SAID WORK POSITIONS OF THE TABLE SO THAT SUCCESSIVE CONTRACTION AND EXTENSION OF THE POWERED MEMBER OSCILLATES THE TABLE FROM ONE WORK POSITION TO THE OTHER WITH MAXIMUM MECHANICAL ADVANTAGE AT THE INITIATION AND CONCLUSION OF SUCH MOVEMENT AND MAXIMUM ANGULAR VELOCITY OF THE TABLE MIDWAY BETWEEN SUCH INITIATION AND CONCLUSION OF THE MOVEMENT. 